add pixi installation method with example

[pablovela5620]

I was having some issues getting glomap installed from source, so I optionally added the pixi installation method.

This is basically like a conda environment but with better reproducibility and a pretty powerful task system. For example, with how it's setup, just doing

pixi run example

complies and installs glomap to the pixi environment (and does not clash with other system packages since its in its own isolated environment like when creating a conda env) downloads and example dataset and runs the glomap mapper.

If one just wants to use glomap, running

pixi shell

activates the environment with glomap correctly installed from source.

I had to slightly modify the Finddependencies.cmake to avoid some cuda + glog errors I was getting when trying to get colmap from fetchcontent. If I didn't modify I would get the following error. Let me know if I'm missing something or if there's some other better way to fix this

/home/pablo/0Dev/repos/glomap/build/_deps/colmap-src/src/colmap/util/logging.h:151:3: note:   candidate expects 2 arguments, 3 provided
ninja: build stopped: subcommand failed

Let me know if this is interesting to you all and if you'd be willing to get this merged! I'm sure it would make getting glomap installed a lot easier for many